title: Integrating nitric oxide into salicylic acid and jasmonic acid/ ethylene plant defense pathways.
abstract: Plant defense against pests and pathogens is known to be conferred by either salicylic acid (SA) or jasmonic acid (JA)/ethylene (ET) pathways, depending on infection or herbivore-grazing strategy. It is well attested that SA and JA/ET pathways are mutually antagonistic allowing defense responses to be tailored to particular biotic stresses. Nitric oxide (NO) has emerged as a major signal influencing resistance mediated by both signaling pathways but no attempt has been made to integrate NO into established SA/JA/ET interactions. NO has been shown to act as an inducer or suppressor of signaling along each pathway. NO will initiate SA biosynthesis and nitrosylate key cysteines on TGA-class transcription factors to aid in the initiation of SA-dependent gene expression. Against this, S-nitrosylation of NONEXPRESSOR OF PATHOGENESIS-RELATED PROTEINS1 (NPR1) will promote the NPR1 oligomerization within the cytoplasm to reduce TGA activation. In JA biosynthesis, NO will initiate the expression of JA biosynthetic enzymes, presumably to over-come any antagonistic effects of SA on JA-mediated transcription. NO will also initiate the expression of ET biosynthetic genes but a suppressive role is also observed in the S-nitrosylation and inhibition of S-adenosylmethionine transferases which provides methyl groups for ET production. Based on these data a model for NO action is proposed but we have also highlighted the need to understand when and how inductive and suppressive steps are used.
authors.affiliation: Molecular Plant Pathology Group, Institute of Environmental and Rural Science, Aberystwyth University Aberystwyth, UK.
authors.forename: Luis A J
authors.initials: LA
authors.lastname: Mur
authors.forename: Elena
authors.initials: E
authors.lastname: Prats
authors.forename: Sandra
authors.initials: S
authors.lastname: Pierre
authors.forename: Michael A
authors.initials: MA
authors.lastname: Hall
authors.forename: Kim H
authors.initials: KH
authors.lastname: Hebelstrup
keywords: ethylenes; jasmonic acid; nitric oxide; pathogens; resistance mechanisms; salicylic acid; signaling pathways